Embodiments of the inventive concept relate generally to electronic memory technologies. More particularly, embodiments of the inventive concept relate to nonvolatile memory devices, memory systems comprising nonvolatile memory devices, and wear leveling methods for nonvolatile memory devices.
Nonvolatile memory is a type of memory that retains stored data when disconnected from power. One popular form of nonvolatile memory is flash memory, which can be found in a wide range of modern electronic devices, such as computers, portable memory drives, home electronics, cellular phones, and digital cameras, to name but a few.
Unlike some other forms of memory, flash memory cannot be rewritten without first performing an erase operation. In other words, before new data can be written to a memory cell of a flash memory device, any old data must be erased from the memory cell. Each block of a flash memory is limited in the number of erase operations that it can undergo before it wears out. This limitation is referred to as erase endurance, and it tends to vary between different flash memories. As an example, many flash memories have an erase endurance of ten thousand to one million erase cycles.
Once a memory block wears out, its memory cells can no longer reliably store data. Accordingly, to avoid errors that can arise from unreliable memory blocks, flash memories often maintain an erase count for each memory block to ensure that the memory blocks are not erased beyond their erase endurance. The erase count can also be used, for instance, to perform wear leveling, which aims to control the distribution of erase operations among different memory blocks. Typically, wear leveling is used to prevent different memory blocks from wearing out at significantly different rates.